Wellbores are formed in subterranean formations for various purposes including, for example, extraction of oil and gas from the subterranean formation and extraction of geothermal heat from the subterranean formation. A wellbore may be formed in a subterranean formation using a drill bit such as, for example, an earth-boring rotary drill bit. Different types of earth-boring rotary drill bits are known in the art including, for example, fixed-cutter bits (which are often referred to in the art as “drag” bits), rolling-cutter bits (which are often referred to in the art as “rock” bits), diamond-impregnated bits, and hybrid bits (which may include, for example, both fixed cutters and rolling cutters). The drill bit is rotated and advanced into the subterranean formation. As the drill bit rotates, the cutters or abrasive structures thereof cut, crush, shear, and/or abrade away the formation material to form the wellbore. A diameter of the wellbore drilled by the drill bit may be defined by the cutting structures disposed at the largest outer diameter of the drill bit.
The drill bit is coupled, either directly or indirectly, to an end of what is referred to in the art as a “drill string,” which comprises a series of elongated tubular segments connected end-to-end that extends into the wellbore from the surface of the formation. Various tools and components, including the drill bit, may be coupled together at the distal end of the drill string at the bottom of the wellbore being drilled. This assembly of tools and components is referred to in the art as a “bottom hole assembly” (BHA).
The drill bit may be rotated within the wellbore by rotating the drill string from the surface of the formation, or the drill bit may be rotated by coupling the drill bit to a downhole motor, which is also coupled to the drill string and disposed proximate the bottom of the wellbore. The downhole motor may comprise, for example, a hydraulic Moineau-type motor having a shaft, to which the drill bit is mounted, that may be caused to rotate by pumping fluid (e.g., drilling mud or fluid) from the surface of the formation down through the center of the drill string, through the hydraulic motor, out from nozzles in the drill bit, and back up to the surface of the formation through the annular space between the outer surface of the drill string and the exposed surface of the formation within the wellbore.
It is known in the art to use what are referred to in the art as a “reamer” devices (also referred to in the art as “hole opening devices” or “hole openers”) in conjunction with a drill bit as part of a bottom hole assembly when drilling a wellbore in a subterranean formation. In such a configuration, the drill bit operates as a “pilot” bit to form a pilot bore in the subterranean formation. As the drill bit and bottom hole assembly advances into the formation, the reamer device follows the drill bit through the pilot bore and enlarges the diameter of, or “reams,” the pilot bore.
After drilling a wellbore in a subterranean earth-formation, it may be desirable to line the wellbore with sections of casing or liner. Casing is relatively large diameter pipe (relative to the diameter of the drill pipe of the drill string used to drill a particular wellbore) that is assembled by coupling casing sections in an end-to-end configuration. Casing is inserted into a previously drilled wellbore, and is used to seal the walls of the subterranean formations within the wellbore. The casing then may be perforated at one or more selected locations within the wellbore to provide fluid communication between the subterranean formation and the interior of the wellbore. Casing may be cemented in place within the wellbore. The term “liner” refers to a casing string that does not extend to the top of a wellbore, but instead is anchored or suspended from inside the bottom of a casing string previously placed within the wellbore.
As casing is advanced into a wellbore, it is known in the art to secure a casing bit to the distal end of the distal casing section in the casing string (the leading end of the casing string as it is advanced into the wellbore). As used herein, the term “distal” means distal to the earth surface into which the wellbore extends (i.e., the end of the wellbore at the surface), while the term “proximal” means proximal to the earth surface into which the wellbore extends. The casing string, with the casing bit attached thereto, optionally may be rotated in tandem with the casing bit as the casing is advanced into the wellbore. In some instances, the casing bit may be configured as what is referred to in the art as a casing “shoe” which is primarily configured to guide the casing into the wellbore and ensure that no obstructions or debris are in the path of the casing, and to ensure that no debris is allowed to enter the interior of the casing as the casing is advanced into the wellbore. In other instances, the casing bit may be configured as a reaming bit, which serves the same purposes of a casing shoe, but is further configured for reaming (i.e., enlarging) the diameter of the wellbore as the casing is advanced into the wellbore. It is also known to employ casing bits that are configured as drill bits for drilling a wellbore. Drilling a wellbore with such a drill bit attached to casing is referred to in the art as “drilling with casing.” As used herein, the term “casing bit” means and includes any type of end cap structure configured for attachment to a distal end of casing as the casing is advanced into a wellbore, and includes, for example, casing shoes, casing reamers, and casing drill bits.
There are instances, however, in which it is desirable to perform what is referred to in the art as a “cleaning” (or “polishing”) process within a previously drilled wellbore prior to positioning casing within the wellbore. As used herein, the phrases “cleaning a wellbore” and “cleaning a section of a wellbore” mean advancing a device (e.g., a bit) through at least a section of a previously drilled wellbore to ensure that the section of the wellbore is at least substantially free of obstructions and has a diameter at least as large as a diameter of the device. In some instances, it may not be feasible or practical to rotate casing as the casing is advanced into a wellbore, and, hence, it is important to ensure that the wellbore is clean prior to advancing the casing into the wellbore. Thus, some drilling operators use a drill string to run a drill bit used to initially drill the wellbore into the wellbore one or more additional times to clean the wellbore. Such processes, however, may be subject to the risk of the drill bit veering off from the initial wellbore (i.e., sidetracking) and starting to form another wellbore.
There remains a need in the art for drilling systems, bits, and methods that may be used for cleaning previously drilled wellbores.